The data is taken from the New England Journal of Medicine vol 329 p437. 1µg of nicotine is the equivalent of sitting in a vaguely smoke filled room for three hours. A cigarette contains about 7mg of nicotine, of which 1mg is absorbed. In other words, 100g of eggplant contains 0.01mg of nicotine, and 10kg of eggplant is equivalent to one cigarette. However, absorbtion rates from ingestion are low and nicotine is quickly metabolized, so the effect isn't nearly the same.